The present invention relates generally to the field of acoustics, and in particular to transducers, to communication and power transmission using vibrations, and to taking sensor readings in deep wells.
A transducer is a device that converts a signal in one form of energy to another form of energy. This can include electrical energy, mechanical energy, electromagnetic and light energy, chemical energy, acoustic energy, and thermal energy, among others. While the term “transducer” often refers to a sensor or a detector, any device which converts energy can be considered a transducer.
Transducers are often used in measuring instruments. A sensor is used to detect a parameter in one form and report it in another form of energy, typically as an electrical signal. For example, a pressure sensor might detect pressure—a mechanical form of energy—and convert it to electricity for display for transmission, recording, and/or as a power source. A vibration powered generator is a type of transducer that converts kinetic energy derived from ambient vibration to electrical energy.
A transducer can also be an actuator which accepts energy and produces movement, such as vibrational energy or acoustic energy. The energy supplied to an actuator might be electrical or mechanical, such as pneumatic or hydraulic energy. An electric motor and a loudspeaker are both actuators, converting electrical energy into motion for different purposes.
Some transducers have multiple functions, both detecting and creating action. For example, an ultrasonic transducer may switch back and forth many times a second between acting as an actuator to produce ultrasonic waves, and acting as a sensor to detect ultrasonic waves and converting them into electrical signals. Analogously, rotating a DC electric motor's rotor will produce electricity, and voice-coil speakers can also function as microphones.
Piezoelectric materials can be used as transducers to harvest even low levels of mechanical energy and convert them into electrical energy. This energy can be suitable for powering wireless sensors, low power microprocessors, or charging batteries. A piezoelectric sensor or transducer is a device that uses a piezoelectric effect to measure pressure, acceleration, strain, or force by converting those physical energies into an electrical charge. The piezoelectric effect is a reversible process in that materials exhibiting the direct piezoelectric effect (generation of an electrical charge as a result of an applied mechanical force) also exhibit the reverse piezoelectric effect (generating a mechanical movement when exposed to an electrical charge or field). Thus, piezoelectric transducers can also work in reverse, turning electrical energy into physical vibrational energy and vice versa. Piezoelectric transducers have the dual advantages of working using low energy levels, and a small physical size. Ultrasonic transducers may be piezoelectric transducers, applying ultrasound waves into a body, and also receiving a returned wave from the body and converting it into an electrical signal.
In drilling and oil well operations, it is often necessary to communicate information (such as sensor data) along a drill pipe string. A drill pipe string consists of connected segments of piping. Often, portions of the well and drill string are not directly accessible via a direct electrical connection. For example, there may be segments that are disjointed and sealed off from each other, making electrical connection between the segments impossible. Since it is desirable to obtain data from deep within wells, passage of the data through these obstacles is a significant issue.
Accordingly, one method and arrangement for powering, controlling, and communicating with sensors at a distance uses acoustic wave energy. The arrangement comprises a transmission arrangement comprising an acoustic signal generator, a receiving arraignment comprising an acoustic signal receiver, a least one sensor which is electrically coupled to the signal receiver, and a waveguide spanning between and engaged to the signal generator and the signal receiver. An acoustical wave preferably comprising a control signal can be generated with the signal generator, the acoustical wave preferably having sufficient strength to provide operating power to the sensor. The acoustical wave is transmitted from the signal generator to the signal receiver through the waveguide. The acoustical wave is received at the signal receiver, and converted into an electrical current optionally comprising a converted control signal. Preferably the electrical current is also used to power a sensor, communication device and/or other devices in the vicinity of the receiving arrangement. A control signal can simultaneously or alternatively be transmitted by the above method, such as by modulating the acoustic wave.
Transmitting and receiving arrangements can comprise piezoelectric transducers, where the signal generator piezoelectric transducer generates an acoustical wave comprising a control signal in response to electrical current applied to it. The signal receiver piezoelectric transducer then receives at least part of the acoustical wave, and converts at least a portion of the received acoustical wave into an electrical current which is then used to power and/or control the sensor. The sensor is not limited to any one sensor, and may detect pressure, temperature, vibrations, sounds, light, or other conditions.
It is possible to power one or more sensors exclusively using electricity generated by the signal receiver piezoelectric transducer, particularly sensors with low power requirements.
In one useful configuration, the transmission arrangement is above ground, while the receiving arraignment and a sensor are below ground, such as in a mine, well, tunnel, or shaft. Waves transmitted from the signal generator to the signal receiver through the waveguide can be used to power and control the sensor below ground. Waves in the reverse direction can transmit sensor data or other data back to the same transmission arrangement, or to a different arrangement provided for that purpose.
Waves can be modulated in a variety of known ways to create the control signal. In a preferred embodiment a continuous wave for transmitting power is selectively modulated when it is desired to send signals or information in addition to or instead of operating power.
A method of transmitting at least one of power and signals along a substrate using angle beam probes can include: providing a transmitting acoustic wedge and a receiving acoustic wedge spaced apart on a substrate and coupled to the substrate at respective interfaces; wherein each acoustic wedge comprises a transition wedge and a transducer comprising a transducer face, wherein the transducer is coupled to the transition wedge, and wherein a transducer face of each transducer is normal to an angle .theta. with regard to the substrate at the respective interface; wherein, in some arrangements: the transducer face of the transmitting transducer of the transmitting acoustic wedge is normal to an angle Θ1 with respect to the respective interface with the substrate, the angle Θ1 in some embodiments between first and second critical angles such that longitudinal waves produced by the transmitting transducer are substantially converted into shear waves in the substrate; in some arrangements the method further comprising producing longitudinal waves at angle Θ1 at the transmitting transducer; in some arrangements, the longitudinal waves producing substantially only shear waves in the substrate, and the shear waves propagating through the substrate until reaching the interface between the substrate and the receiving acoustic wedge; in some arrangements, energy from the shear waves providing acoustical wave energy which reaches the receiving transducer of the receiving acoustic wedge; and the receiving transducer converting at least a portion of said acoustical wave energy into electrical energy.
In alternative arrangements, shear waves created by angled longitudinal waves can be used to send power and/or signals down the length of a substrate such as a steel pipe in an oil well.
A transmitting acoustic wedge and a receiving acoustic wedge can be provided spaced apart on a substrate and coupled to the substrate at respective interfaces. In one embodiment each acoustic wedge comprises a transition wedge and a transducer comprising a transducer face. The transducer is coupled to the transition wedge, and a transducer face of each transducer is normal to an angle .theta. with regard to the substrate at the respective interface. A preferably planar transducer face of the transmitting transducer of the transmitting acoustic wedge is normal to an angle Θ1 with respect to the respective interface with the substrate, the angle Θ1 being between first and second critical angles such that longitudinal waves produced by the transmitting transducer are substantially converted into shear waves in the substrate.
One method further includes producing longitudinal waves at angle .theta..sub.1 at the transmitting transducer. The longitudinal waves produce only or substantially only shear waves in the substrate, and the shear waves propagate through the substrate until reaching the interface between the substrate and the receiving acoustic wedge. Energy from the shear waves provides acoustical wave energy which reaches the receiving transducer of the receiving acoustic wedge, and the receiving transducer converts at least a portion of said acoustical wave energy into electrical energy. The energy can be used to transmit power and/or signals to sensors or other electronics. This is particularly useful for sensors and electronics deep underground.
In some arrangements, most or all of the shear wave energy which reaches the receiving acoustic wedge converts back to longitudinal waves at the receiving acoustic wedge. The receiving transducer of the receiving acoustic wedge then receives at least a portion of the longitudinal waves and converts at least a portion of said longitudinal waves into electrical energy.
In previously known arrangements, the substrate comprises metal(s) such as steel, and the transition wedges are acrylic. The substrate may be a metal pipe, such as in an oil well.
In some arrangements, wedge, transducer, and substrate methods and apparatus can also be used to send signals in the reverse direction from the receiving acoustic wedge to the transmitting acoustic wedge. The step of sending signals in the reverse direction comprises the receiving transducer generating waves at an angle with respect to the respective interface with the substrate, the angle being between first and second critical angles, and the waves propagating through the substrate to the receiving acoustic wedge.
In another arrangement, the transition wedge of the transmitting acoustic wedge includes a generally slanted edge which is normal to an angle .theta..sub.1 with respect to the respective interface with the substrate. Typically a flat or planer face of a transducer is fixed to the slanted edge so that the transducer face is oriented in the same direction, i.e. on the same plane, as the slanted edge. In practice, the orientation of the transducer will often be selected by selecting a proper angle for the slanted edge. Thus, preferably, the slanted edge is normal to an angle .theta..sub.1 is between first and second critical angles such that longitudinal waves produced by the transmitting transducer are substantially converted into shear waves in the substrate.
Though the substrate may be a large item with a large surface area and varied shape, the angle of the substrate where the respective acoustic wedges and transducers are located is a key angle of concern in selecting longitudinal wave angles. Typically this will be the angle at an interface between each acoustic wedge and the substrate.
Proper angles for launching longitudinal waves to produce shear waves in a substrate can be determined using Snell's law. The angle Θ1 between first and second critical angles can be the longitudinal wave launch angle Θ1Longitudinal. Thus, the method of the invention can include the step of determining Θ1Longitudinal using the relationship:
      arcsin    ⁡          (                        V                      1            ⁢            Longitudinal                                    V                      2            ⁢            Longitudinal                              )        <      θ          1      ⁢      Longitudinal        <      arcsin    ⁡          (                        V                      1            ⁢            Longitudinal                                    V                      2            ⁢            Shear                              )      
wherein V1Longitudinal is the longitudinal wave speed in the transition wedge, V2Longitudinal is the longitudinal wave speed in the substrate, and V2Shear is the shear wave speed of the substrate. This is a method for determining the angle and orientation of the transducers and/or slanted edges supporting the transducers.
Longitudinal wave are waves where the displacement of the medium is in the same direction as, or the opposite direction to, the direction of travel of the wave. Mechanical longitudinal waves are also called compression waves, because they produce compression and rarefaction when traveling through a medium.
A shear or transverse wave is a moving wave that consists of oscillations occurring perpendicular (i.e. at right angles) to the direction of energy transfer. If a shear wave is moving in the positive x-direction, its oscillations are in up and down in the y-z plane. With transverse waves in matter, the displacement of the medium is perpendicular to the direction of propagation of the wave. A ripple in a pond or a wave on a string are examples of transverse waves.
Power and Communication Transmission Through a Surface Via Angled Waves
For digital acoustic communication and acoustic power transfer along a substrate, continuous acoustic waves are transmitted along the substrate channel between a pair of electromechanical transducers. This technology allows remote sensing of sealed environments. A better understanding of wave propagation will allow for systems that will operate more efficiently and can act over larger ranges. Although guided wave modes in the substrate have been more extensively studied than bulk waves, wedge-introduced bulk waves have shown the potential to outperform them in some situations. Advantages include directionality of the wave field and simplicity of implementation; to excite guided modes, it is in many cases necessary to use numerous transducers, while when using wedge introduced bulk waves, a pair will often be sufficient, especially over short range.
As mentioned, in drilling and oil well operations, it is often necessary to communicate information (such as sensor data) along a drill pipe string where portions of the well and drill string are not directly accessible via a direct electrical connection. For example, there may be segments that are disjointed and sealed off from each other, making electrical connection between the segments impossible. An alternative aspect of the present invention is therefore an improved means of passing both power and data through drill pipe strings, including strings having blocked off sections, using acoustic waves sent through the pipe itself.
The system can simultaneously transmit both digital information and/or power, preferably in both directions, through the wall of a pipe or other analogous substrate using ultrasound from an angle beam probe. The angle beam probe may comprise transducers, such as an ultrasonic piezoelectric transducers.
Similar power communication systems can be implemented using longitudinal waves by using magnetostrictive means as well. Magnetostrictive materials can convert magnetic energy into kinetic energy, and vice versa.
One transmission system, shown schematically in FIG. 1, consists of two acoustic wedges 40,50, which may be sending and receiving acoustic wedges. Each acoustic wedge preferably includes a transition wedge 44,54 and a transducer 41,51. Each transducer preferably includes a generally planar face 47,57. Each transition wedge preferably has at least one slanted edge 46,56. The planar face of a transducer may be fixed to a slanted edge to fix and orient the planar face at a given angle. The angle of the slanted edge, or other aspects of the shape of the transition wedges, may be selected in order to support a transducer at a selected angle. A transition wedge may, in some embodiments, resemble a rectangular solid with a corner sliced off to provide the slanted edge, although the invention is not limited to any particular shape. Typically a bottom side of each transition wedge 44,54 is engaged to the substrate 60. The interface 48,58 of the substrate and the wedges should be as seamless as possible for sending and receiving wave energy. A signal sender/receiver, typically a transducer 41,51, is fixed to a slanted edge on the transition wedge so that a flat face of the transducer is at an intermediate angle with regard to the plane of the substrate 75 at the interface 48,58. The acoustic wedges may also be triangles or other shapes. Various arrangements to provide transducers at an angle with regard to the substrate are within the scope and spirit of the invention. In one embodiment a surface transducer A 41 is located above ground, and a second transducer B 51 is located underground.
The first acoustic wedge 40 sends longitudinal waves 70 launched by transmitting transducer a 41 through a transition block or wedge 44 into a plate or cylindrical shell 60 (e.g., pipe) at an angle such that only transverse (shear) waves 75 are produced in the plate/shell 60. The launch angle in the wedge 40,50 is selected such that it is between the first and second critical angles, so that substantially only shear waves will be produced in the wall 60. These shear waves 75 propagate down the wall 60 to a second acoustic wedge 50 which is angled such that the received shear waves 75 are converted back into longitudinal waves 70 within the transition wedge 54. The longitudinal waves 70 are then captured by the second receiving acoustic transducer B 51. In all embodiments, sending and receiving transducers may be the same or different. In one embodiment above-ground sending 41 and below-ground receiving 51 transducers are essentially the same other than their positions in the system. In some embodiments both sending and receiving transducers send and receive acoustic wave signals.
A portion of the acoustic energy captured by the receiving transducer B 51 can be harvested to produce electric energy in order to power sensors 90 or other devices 90 located in the same region as the second acoustic wedge 50 and transducer B 51. Referring to FIG. 1, the data generated by the sensors 90 near “receiving” transducer B may be sent back to the first “sending” transducer A 41. The data may be sent back digitally from transducer B 51 along a wall 60 to transducer A 41, where the data may be properly stored, displayed, or retransmitted. Data from the vicinity of transducer B 51 may also be sent elsewhere, and by other known methods. Data may also be sent back using shear waves using the method above in the reverse direction.
FIG. 2 is a background illustration and equation to help explain the concept of critical angles.
The critical angle is the angle of incidence above which total internal reflection occurs. The angle of incidence is typically measured with respect to the normal at the refractive boundary. Total internal reflection occurs when a propagating wave strikes a medium boundary at an angle larger than a particular critical angle with respect to the normal to the surface. If the refractive index is lower on the other side of the boundary and the incident angle is greater than the critical angle, the wave cannot pass through and is entirely reflected. This is particularly common as an optical phenomenon, where light waves are involved, but it occurs with other types of waves, such as electromagnetic waves in or sound waves.
When a wave crosses a boundary between materials with different refractive indices, the wave will be partially refracted at the boundary surface, and partially reflected. However, if the angle of incidence is greater than the critical angle—if the direction of propagation or ray is closer to being parallel to the boundary—then the wave will not cross the boundary and instead be totally reflected back internally. This can only occur where the wave travels from a medium with a higher refractive index to one with a lower refractive index. For example, it will occur with light when passing from glass to air, but not when passing from air to glass.
Consider a light ray passing from glass into air or. The light emanating from the interface is bent towards the glass. When the incident angle is increased sufficiently, the transmitted angle (in air) reaches 90 degrees. It is at this point no light is transmitted into air. The critical angle Θ1Critical is given by Snell's law. FIG. 2 Illustrates an analogous relationship with a ray of light passing from water into air.
FIG. 3 shows the relationship between the incident angle of the angular longitudinal wave and the relative amplitudes of the refracted and/or mode converted longitudinal, shear, and surface waves that can be produced in the substrate. The method of the invention makes use of the strong shear waves which can be created by using the proper incident angle between the first and second critical angles.
Using Snell's law, the refraction angles (e.g. angles Θ1 and Θ2 in FIG. 1) for use in applicable embodiments may be determined from:
            sin      ⁢                          ⁢              θ                  1          ⁢          Longitudinal                            V              1        ⁢        Longitudinal              =                    sin        ⁢                                  ⁢                  θ                      2            ⁢            Shear                                      V                  2          ⁢          Shear                      =                            sin          ⁢                                          ⁢                      θ                          2              ⁢              Longitudinal                                                V                      2            ⁢            Longitudinal                              =                        sin          ⁢                                          ⁢                      θ                          1              ⁢              Shear                                                V                      1            ⁢            Shear                              
To produce only a shear wave in the plate/shell/pipe 60, the longitudinal launch angle Θ1Longitudinal has to be between the first and second critical angles, which will be produced as long as the longitudinal wave in the launch material has a sound speed less than the shear wave speed of the steel:
      arcsin    ⁡          (                        V                      1            ⁢            Longitudinal                                    V                      2            ⁢            Longitudinal                              )        <      θ          1      ⁢      Longitudinal        <      arcsin    ⁡          (                        V                      1            ⁢            Longitudinal                                    V                      2            ⁢            Shear                              )      
For example, one available launch material in is acrylic (which may be Perspex), which has a longitudinal wave speed of V1Longitudinal acrylic=2,730 m/s. The first critical launch angle is found by setting Θ2Longitudinal to 90°, giving the first critical angle:
      sin    ⁢                  ⁢          θ              1        ⁢        Longitudinal        ⁢                                  ⁢        First        ⁢                                  ⁢        Critical              =            V              1        ⁢        Longitudinal                    V              2        ⁢        Longitudinal            and the second critical launch angle is found by setting Θ2Shear to 90°, giving the second critical angle
      sin    ⁢                  ⁢          θ              1        ⁢                                  ⁢        Longitudinal        ⁢                                  ⁢        Second        ⁢                                  ⁢        Critical              =            V              1        ⁢        Longitudinal                    V              2        ⁢        Shear            
If, for example, the wall used with the above acrylic launch wedge is made of steel with a shear wave speed of V2Shear=3,250 m/s, and a longitudinal wave speed of V2Longitudinal=6,100 m/s, then these angles are:
            θ              1        ⁢                                  ⁢        Longitudinal        ⁢                                  ⁢        First        ⁢                                  ⁢        Critical              =                  arcsin        ⁡                  (                                    V                              1                ⁢                Longitudinal                                                    V                              2                ⁢                Longitudinal                                              )                    =                        arcsin          ⁡                      (                          2.730              /              6100                        )                          =                  26.57          ⁢          °                                θ              1        ⁢                                  ⁢        Longitudinal        ⁢                                  ⁢        Second        ⁢                                  ⁢        Critical              =                  arcsin        ⁡                  (                                    V                              1                ⁢                Longitudinal                                                    V                              2                ⁢                Shear                                              )                    =                        arcsin          ⁡                      (                          2.730              /              3250                        )                          =                  57.11          ⁢          °                    
Another material that can be used for higher temperature applications is Teflon, with a longitudinal wave speed of 1,372 m/s, and corresponding first and second critical angles of 13.46 degrees and 24.96 degrees, respectively.
So, for Θ1Longitudinal First Critical<Θ1<Θ1Longitudinal Second Critical, only shear waves at an angle Θ2Shear will be present in the communications channel. In addition, this system can also be adjusted by launching pure shear waves at angle Θ1Shear using a shear wave transducer in addition to or instead of the above arrangement starting with angled longitudinal waves. Note that there will also be two waves generated in at least the transmitting wedge 44,54, due to reflection, Θ1Longitudinal and Θ1Shear. These reflected waves are either scattered or absorbed by the other wall of the wedge.
Many different channel modulation techniques are suitable for these arrangements. Non-limiting examples include traditional single-carrier modulations such as amplitude modulation (AM), frequency modulation (FM), ON-OFF Keying (OOK), amplitude-shift keying (ASK), phase-shift keying (PSK), differential phase-shift keying (DPSK), frequency-shift keying (FSK) and quadrature amplitude modulation (QAM).
Multi-carrier modulations such as orthogonal frequency-division multiplexing can also be used and will, in general, provide higher data rates for the channel. Multi-carrier techniques offer the ability to optimize the transmission for the specific transfer function that the channel presents though the use of bit loading. In bit loading each subcarrier uses a modulation type that provides the highest data rate given the signal-to-noise ratio (SNR) of that particular subcarrier channel. Multi-carrier techniques can instead or in addition include power loading, in which the transmit power of each subcarrier is also adjusted to optimize the data throughput over all subcarriers given an overall power budget.
FIG. 4 shows a side view of an exemplary acoustic wedge mounted on a ⅞″ diameter, 0.7 inch thick steel pipe substrate. The arrangement includes a transition wedge and a mounted transducer. FIG. 5 shows a section of the same pipe with a pair of acoustic wedges mounted thereon for use with the invention.
FIGS. 6 and 7 are computer generated images showing shear wave propagation. The shear waves are launched via a longitudinal wave sent through an acrylic wedge into a 0.7 inch (17.78 mm) thick submerged steel plate substrate. In both figures the Wedge is the triangle at top left, and the steel plate substrate is the thick horizontal line at the center with water above and below it. FIG. 6 shows the (pressure) 0.3 in the beam and wedge. FIG. 7 shows the xy deviatoric stress (the log of the Von Mises stress) in the beam and wedge. Both figures show the (pressure) 0.3 in the water.
FIGS. 8-10 are plots of the log of the amplitude of the pressure in the steel substrate and acrylic wedge at three different frequencies: 0.5 (FIG. 8), 1.0 (FIG. 9), and 2.25 (FIG. 10) MHz. It makes the standing wave in the solids more clear. Also the beam is now 8″ instead of 3″.